setText和OnClickListener不起作用

Question

我是Android的新手，所以我遇到了很多问题。我要做一个简单的程序，它可以从edittext中获取值，并通过单击按钮将其打印在textview中。这是我的代码：

该计划说，不幸的是它停止了工作。但是，当我从setOnClickListener删除最后几行时，它工作正常。我也只用setText测试过它。它也不起作用。谢谢。 logcat的：

XML：

Answer 1

您的代码应该在PlaceHolderFragment中，如下所示..

public class PlaceHolderFragment extends Fragment {
    private EditText et;
    private Button b;
    private TextView tv;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container,
            false);
        return rootView;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onActivityCreated(savedInstanceState);

        et=(EditText) getView().findViewById(R.id.EditText1);
        b = (Button) getView().findViewById(R.id.Button1);
        tv = (Button) getView().findViewById(R.id.textView3);
        b.setOnClicklistener(new OnClickListener(){
            @Override
            public void onClick(View arg0){
                tv.setText("Pressed");
            }
        });
    }
}

并从onCreate()

中删除这些代码

et=(EditText) findViewById(R.id.EditText1);
b = (Button) findViewById(R.id.Button1);
tv = (Button) findViewById(R.id.textView3);
b.setOnClicklistener(new OnClickListener(){
    @Override
    public void onClick(View arg0){
        tv.setText("Pressed");
    }
});

试试这个......

<强>更新

1. activity_main.xml中



1. fragment_main.xml



1. MainActivity.java

import android.support.annotation.Nullable;
import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        private EditText et;
        private Button b;
        private TextView tv;

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }

        @Override
        public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            // TODO Auto-generated method stub
            super.onActivityCreated(savedInstanceState);

            et = (EditText) getView().findViewById(R.id.editText1);
            b = (Button) getView().findViewById(R.id.button1);
            tv = (TextView) getView().findViewById(R.id.textView1);
            b.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View arg0) {
                    tv.setText("Pressed");
                }
            });
        }
    }
}

输出：

Answer 2

我认为您分享的xml是fragment_main而不是activity_main。确保你正在膨胀正确的xml并仅引用它的控件... NULL Pointer Exception仅由于此而生成。

根据您的代码， textview，edittext和按钮必须位于activity_main.xml

 et=(EditText) findViewById(R.id.EditText1);
 b = (Button) findViewById(R.id.Button1);
 tv = (TextView) findViewById(R.id.textView3);

确认。

如果控件位于frgament_main中，则需要使用以下代码：

public class PlaceHolderFragment extends Fragment {
    private EditText et;
    private Button b;
    private TextView tv;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container,
            false);

        et=(EditText) rootView.findViewById(R.id.EditText1);
        b = (Button) rootView.findViewById(R.id.Button1);
        tv = (TextView) rootView.findViewById(R.id.textView3);
        b.setOnClicklistener(new OnClickListener(){
            @Override
            public void onClick(View arg0){
                tv.setText("Pressed");
            }
        });
        return rootView;
    }

}